Epoxy coatings and flooring materials are well know and have gained commercial acceptance as protective and decorative coatings for steel, aluminum, galvanizing, wood and concrete in maintenance, marine, construction, architectural, aircraft and product finishing markets. The basic raw materials used to prepare these coatings generally comprise as essential components (a) an epoxy resin, (b) a hardener and (c) a pigment or aggregate component.
The epoxide resins are those having more than one 1,2-epoxy group per mole and may be saturated or unsaturated, aliphatic, cycloaliphatic, or heterocyclic. The epoxide resins generally contain glycidyl ester or glycidyl ether groups and have a weight per epoxide of from 100 to 2000. The hardener is usually chosen from the general classes of aliphatic amines or aliphatic amine adducts, polyamides, polyamidoamines, cycloaliphatic amines, aromatic amines, Mannich bases, ketimines and carboxylic derivatives. Pigments or aggregates include titanium dioxide and other inorganic and organic color pigments, silica, barium sulfate, magnesium silicate, calcium silicate, fumed silica, garnet, feldspar, carbon black and the like.
Known epoxy based flooring and coating materials often contain several components in addition to the epoxy resin, hardener and pigment/aggregate. These include such additives as nonreactive and reactive diluents including mono- and di-epoxides, plasticizer, bituminous and asphaltic extenders, adhesion promoters, suspending agents and thixotropes, surfactants, corrosion inhibitors, ultraviolet light stabilizers, catalysts and rheological modifiers.
Both the resin and hardener components may also contain volatile organic solvents whose primary function is to lower viscosity thereby providing a consistency suitable for spray application with conventional air, airless and electrostatic spray equipment.
Epoxy based protective coatings represent one of the most widely used methods of corrosion control. They are used to provide long term protection of steel, concrete, aluminum and other structures under a broad range of corrosive conditions, extending from atmospheric exposure to full immersion in strongly corrosive solutions. For over 20 years, these coatings have been formulated from either a solid or liquid epoxy resin cured with an aliphatic polyamine or polyamide resin e.g., Shell Epon 1001 or Epon 828 epoxy resins cured with diethylene triamine (DETA) or Versamid 100 series polyamides. In typical two package coating systems, the epoxy resin component is usually the vehicle for pigment grinding and dispersion of other aggregates and various additives.
Epoxy based protective coatings possess many properties which make them desirable as coating materials. They are readily available and are easily applied by a variety of methods including spraying, rolling and brushing. They adhere well to steel, concrete and other substrates, have low moisture vapor transmission rates and act as barriers to water, chloride and sulfate ion ingress, provide excellent corrosion protection under a variety of atmospheric exposure conditions and have good resistance to many chemicals and solvents.
Epoxy based materials are also formulated as surfacers or flooring materials primarily for application over concrete. One commercially successful epoxy based flooring material utilizes liquid bisphenol A epoxy resin and a modified aliphatic polyamine combined with graded silica sand aggregate as a third component. It can be spray applied and has excellent compressive, tensile and flexural strength, good resistance to impact and abrasion and resists a wide variety of chemicals and solvents.
Another commercially successful epoxy based flooring material described in U. S. Pat. No. 3,794,609, utilizes liquid bisphenol A epoxy and a mixture of powdered methylene dianiline (MDA) and graded silica sand as the second component. The composition has excellent resistance to organic and inorganic acids and a wide variety of chemicals and solvents. However, MDA has recently been identified as a carcinogen and its manufacture and use are being regulated. Further, MDA cured epoxies are not very color stable and darken quickly.
The resistance of epoxy based flooring and coating materials to attack by solvents such as acetone and methanol can be poor. The properties of an epoxy resin based film are dependent on the type of epoxy resin and hardener, the chemical nature of the cure linkage and extent of crosslinking relative to chain extension and cross link density. The most important commercial cure mechanisms use aliphatic amines, polyamides, polyamidoamines, aromatic amines and carboxylic derivatives. Unfortunately, amines and carboxylic derivatives result in cured materials which are generally sensitive to acid and hydrolyric degradation. The structural basis for this susceptibility, when using amine hardeners, is the presence of the substituted nitrogen group in the matrix which can be protonated by acid and undergo a series of degradation reactions. In the case of carboxylic acid derived hardeners, the cured material contains ester linkages which are subject to hydrolysis catalyzed by both acid and base.
Epoxy based coating and flooring materials generally do not have good resistance to weathering in sunlight. While such coatings maintain their chemical and corrosion resistance, exposure to the ultraviolet light component of sunlight results in a surface degradation phenomenon known as chalking which changes both the gloss and color of the original coating. Where color and gloss retention is desired or required, epoxy protective coatings are typically topcoated with a more weatherable coating i.e. an alkyd, vinyl or aliphatic polyurethane coating. The end result is a two or sometimes three coat system which provides corrosion resistance and weatherability, but which is also labor intensive and expensive to apply.
A growing emphasis on compliance with government environmental and health hazard regulations has prompted coating and flooring material manufacturers and end users to evaluate new coating technologies. The Clean Air Act sets limits on both the type and amount of volatile organic compounds (VOC) and has resulted in research directed to higher solids, solventless and waterborne protective coating systems. In addition, as part of the Resource Recovery and Conservation Act, the Environmental Protection Agency has established minimum national standards for the management of hazardous waste. Part of these standards deals with the prevention of waste releases into soil and groundwater through chemically resistant coating, lining and flooring materials in the form of secondary containment structures.
Thus, while epoxy based coating and flooring materials have gained wide commercial acceptance, the need nevertheless remains for epoxy based materials with improved color and gloss retention, better chemical and corrosion resistance, and improved resistance to mechanical abuse. New epoxy coating and flooring materials are needed to comply with new governmental environmental and health hazard regulations. Epoxy coatings and flooring materials with improved color and gloss retention are needed wherever they may be exposed to sunlight. An epoxy coating which doesn't chalk and does not require a weatherable topcoat is desirable. Coating and flooring materials with improved chemical, corrosion, impact and abrasion resistance are needed for both primary and secondary chemical containment structures, for protecting steel and concrete in chemical, power generation, railcar, sewage and waste water treatment, and paper and pulp processing industries. Improved epoxy based flooring materials are needed in industrial environments such as shipping and receiving docks where heavy impact loading can be anticipated, for floors which must be repeatedly cleaned with steam and aggressive chemicals, such as those found in food processing, meat packaging and beverage industries and where spills of caustic, acid and highly reactive chemicals cannot be avoided.
Heretofore, epoxy coatings with improved weatherability have been obtained by modification with acrylic resin or by curing inherently weatherable epoxide resins i.e., sorbitol glycidyl ethers, hydrogenated reaction products of bisphenol A and epichlorhydrin, and more recently the epoxy functional coetherified melamine resins from Monsanto with polyamide, cycloaliphatic amine or carboxyl functional acrylic or polyester resins. Another approach has been to use epoxidized polyester resins in combination with certain carboxyl functional vehicles. While these coatings exhibit improved weatherability, their chemical and corrosion resistance is generally inferior to the epoxy resin based coatings previously described.
Epoxy based flooring materials with improved chemical resistance have been developed from epoxy novalac resins and modified cycloaliphatic and aromatic amine hardeners. Epoxy novalac based flooring materials generally cannot be sprayed at 100% solids because of their high viscosity. Aromatic amine hardeners, i.e. methylene dianiline and diethyltoluene diamine are either carcinogenic or suspect carcinogens. These materials generally have excellent chemical resistance, however, their weatherability is very poor. Discoloration may often occur indoors.
Therefore, it is an object of the present invention to provide modified epoxy based coatings with improved chemical, corrosion and weathering resistance.
Another object of this invention is to provide solventless, modified epoxy based flooring materials with improved resistance to weathering and improved solvent, acid and base resistance and which exhibit high tensile and compressive strength and excellent resistance to impact and abrasion.